The government will give tax breaks to gay married couples in a move that is likely to intensify the row within the Conservative party over David Cameron's plans to redefine marriage.

People in same-sex marriages will receive the same tax benefits as everyone else, a Treasury source confirmed. But the development is likely to irk some Tory MPs, according to Bernard Jenkin, who is backing the bill and calling for his colleagues to support the government.

Peter Bone, Tory MP for Wellingborough, said he understood the logic of giving tax breaks to people in gay marriages, but believed there were consequences to the changes that had not been thought through.

He said: "It has been rushed through parliament in similar fashion to the Dangerous Dogs Act. What does this mean for royalty? To what teachers say in schools, for example? It is also unequal in that those in homosexual relationships will be allowed civil partnerships as well which are not permitted for heterosexuals.

"I think the only thing to do is put it to a referendum. We are having one on Europe in 2017 so why not ask this question as well?"

Nick de Bois MP, a senior Tory who is against the bill, said that there was no reason to redefine marriage in order to give tax breaks for same-sex couples. He also criticised the government for not yet delivering the tax changes that would support marriage, a move that was missing from the last budget and is not expected in this year's either.

De Bois, the MP for Enfield North, said: "There is no reason why civil partnerships should not get the same tax breaks. Had the government stuck to their manifesto commitment on tax supporting marriage, they could have legislated for tax changes that would have, of course, benefited civil partnership. To suggest otherwise is disingenuous, and to delay tax changes in favour of prioritising the redefinition of marriage shows they have their priorities wrong."

The prime minister is allowing his backbenchers a free vote on moves to redefine marriage and allow religious groups to conduct same-sex weddings.

Writing in the Observer, Baroness Neuberger, a senior rabbi at the West London Synagogue and a crossbench peer, praised all the party leaders for backing the change, adding: "At the moment, I am legally prevented from doing something that my conscience tells me should not only be permitted, but positively celebrated."

However, Cameron's stand could prove dangerous as he has tied his party's reputation to changing the law, declaring he supports gay marriage "because I am a Conservative".

In reality, up to 200 of the prime minister's 303 MPs are likely to refuse to back the changes next week. Those opposed to the bill point to a ComRes poll showing that one in five Tory voters will not support the party at a general election if it backs gay marriage. The loss of a fifth of its support would force it out of power.It was reported last week that Conservative MPs and constituency chairmen are having to handle hundreds of complaints from grassroots activists.

Downing Street has been working hard to curb dissent in the cabinet amid signs that Iain Duncan Smith, the work and pensions secretary, could support the measure.

Owen Paterson, the environment secretary, is expected to vote against it. Among the Tory MPs opposing the bill are 19 who have signed up to the campaign group Coalition for Marriage, while Liam Fox has described it as "ill thought through and constitutionally wrong".

A Treasury spokesman said: "We are still committed to recognising marriage in the tax system during the course of this parliament."